This invention relates to optical communication systems and, more particularly, to an optical internet router apparatus and operating method which uses optical (message) tags to send and receive commands and responses to/from a source router to establish, maintain, and change an internet path to a destination router.
In an all optical internet (OI), signal conversion from optics to electronics should be avoided if possible, and if absolutely necessary it should take place in as few points as possible. Conversion of signals from electronics to optics should also be minimized, except possibly at the source where the original signal entering the network may be in electronic forms. At the destination where the end devices such as PCs and/or internet servers are electronic devices, however, conversion from optics to electronics are unavoidable.
In present routers, when the signal is transported in optical from (such as when received from an optical fiber) it is first converted to electronic form before being processed at the router. Electronic signals (such as Internet""s IP packets) are usually buffered and queued for processing at the router (such as for routing and error processing). Finally, the electronics signal is converted back to optics for transmission to the next router in the network. Conversion from optics to electronics is expensive in addition to requiring bulky equipment. More importantly, the network performance such as delay as experienced by the end users is degraded (this as a result of buffering and processing at the routers).
In an optical internet, the conversion from optics to electronics and vice versa should be minimized so that not only the task of information exchange and transport can be accomplished at lower cost, but also to improve network performance. In our pending patent application entitled xe2x80x9cDynamically Assignable Optical Signal Access Control Apparatus,xe2x80x9d filed on Oct. 16, 1998, wavelength routing and performance optimization is accomplished through periodic observation of buffer contents at the multiplexer. In that invention, multiple wavelengths can be allocated on a path so that conversion back to electronics in the network is minimized and, furthermore, network resource usage is optimized through proper utilization of wavelengths among source and destinations.
A straightforward method for dealing with performance issues in an internet is for each router/cross-connect to have a dedicated wavelength to all other routers/cross-connects (possible destinations for traffic from each router). Using this approach, and coupled with the technique proposed in our previously referenced patent, performance problems can be minimized. However, currently only a few (in the order of 10-100) wavelengths can be wavelength division multiplexed (WDM) on an optical fiber. If WDM was not a limitation, theoretically it would be possible to establish a dedicated wavelength between all source/destination router pairs in the network. For example, in a network with say 100 routers, 100xc3x97(100xe2x88x921)/2=4950 wavelengths would be required to connect each router with all other routers of the network. For a large network (such as consisting of possibly thousands of routers) the number of wavelengths at each router (or cross-connect) rises rapidly and currently not feasible to be implemented, if wavelength re-use is not permitted.
What is needed is an improved optical packet routing technique that does not require the use of dedicated source/destination wavelengths.
In accordance with the method and apparatus of our invention, an optical internet router apparatus uses optical tags to send command and response messages between routers of an optical network for establishing, maintaining or changing a packet data connection over the network between a source router and a destination router. The optical router comprises (1) optical tag apparatus for optically reading a message and writing a message modulated on one or more wavelengths, which are used for communicating with another router of a network connection, the control message being modulated onto the one or more wavelengths using a secondary modulation which is different from a primary modulation used to modulate packet data; and (2) a controller responsive to a received read message for controlling a network connection at this router, and for generating a network control message to be written by the optical tag apparatus, the generated message controlling a network connection to said another router. The controller is also responsive to a read status response message from the optical tag apparatus, for determining a network connection status at said another router, and can generate a local status response message to be written by the optical tag apparatus to indicate a status at this router.
According to one feature, the router uses messages such as (1) a xe2x80x9cno-changexe2x80x9d message indicating that no change is required in the network connection, (2) a Command To Reassign (CTR) message identifying a change to be made in the network connection, and (3) a response message indicating a response to a previously received message. According to another feature, messages may be sent (1) periodically based on a predetermined time interval, (2) continuously, and (3) in response to a predefined condition at a router in the network.